1. Field of the Invention
This invention relates to a chip-like inductance element, and more particularly relates to a chip-like inductance element which has a cylindrical shape or a shape of a rectangular parallelepiped.
2. Description of the Prior Art
The prior art will be explained by reference to FIGS. 6 through 8 and FIG. 2 according to the present invention.
FIG. 6 is an enlarged perspective view of a magnetic sleeve 31 according to the prior art which the present applicant has proposed in Japanese Utility Model Application No. 60-156,489 (1985).
As is apparent from FIG. 6, a hole 37 is formed in a nearly central portion in both end surfaces 35, 35 of the magnetic sleeve 31. Electrode layers 33, 33' are continuously printed or coated on the circumference of the hole in the both end surfaces 35, 35 and on the entire surfaces of both side surfaces 36, 36 of the magnetic sleeve. Such a magnetic sleeve 31 wherein the electrode layers 33, 33' are coated on the entire surfaces of the both side surfaces 36, 36 other than the end surfaces 35, 35 in which the hole 37 is formed, and the shape of the both side surfaces 36, 36 is square will be called a square magnetic sleeve. On the other hand, a magnetic sleeve in FIG. 5 according to an embodiment of the present invention will be called a rectangular parallelepiped-type magnetic sleeve 1' for the purpose of discrimination. FIG. 2 is an enlarged perspective view of a drum-like magnetic bobbin 9 according to the present invention, which will be used for the convenience of explaining the prior art. As is apparent from FIG. 2, a coil winding 21 is wound on the drum-like magnetic bobbin 9. Guide grooves 19, 19 for drawing out coil winding terminals are formed in side portions of end flanges 11, 11 of the drum-like magnetic bobbin. Also, conductive films 17, 17 are printed or coated on both end surfaces 13, 13 of the end flanges 11, 11. Coil winding terminals 15, 15 are drawn out through the guide grooves 19, 19, and are folded and fixed on the conductive films 17, 17. Such a drum-like magnetic bobbin 9 is fitted in the hole 37 in the square magnetic sleeve 31 in FIG. 6. A production method for obtaining a desired chiplike inductance element will be briefly described by reference to FIGS. 7 and 8. FIG. 7 is an enlarged crosssectional view taken along line VII--VII in FIG. 6 showing a state in which the drum-like magnetic bobbin 9 is inserted in the hole 37 of the square magnetic sleeve 31. Hereafter, for the convenience of explanation, the explanation will be made about the upper coil winding terminal 15. The situation is the same for the lower coil winding terminal 15. A large circular conductive metal plate 43 which is larger than the hole 37, and on which a solder layer 39 has previously been formed is prepared. A suitable flux is coated on a portion where solder connection is to be performed before performing solder connection. Then, the solder layer 39 is faced down and the conductive metal plate 43 is heated from above to fuse the solder layer 39, and thus unified simultaneous solder connection of the drawn-out coil winding terminal 15, the conductive film 17, the electrode layer 33 around the hole and the conductive metal plate 43 is performed. After finishing the desired solder connection, an insulating layer 45 is coated (see FIG. 8). As described above, a chip-like inductance element 27 can be obtained.
Q value is generally used for representing the characteristic of an inductance element. The Q value determines the frequency selection characteristic of a tuning circuit, such as an L-C parallel circuit. It is known that when the Q value is higher, the frequency selection characteristic becomes better. It has become clear, however, that in some cases, the Q value of the chip-like inductance element 27 obtained as described above decreases. The present inventors have found, after several analyses and investigations on the causes of the decrease of the Q value, that the decrease of the Q value is due to the following causes (see FIGS. 7 and 8).
(a) Chemical effect on the coil winding such that the flux flows into the hole 37 from a gap 38 formed between the square magnetic sleeve 31 and the drum-like magnetic bobbin 9 during solder connection to adhere to the coil winding 21.
(b) The electrode layers 33, 33' are printed or coated around the hole 37 in the end surfaces 35, 35 of the square magnetic sleeve, so the electrode layers 33, 33' occasionally adhere to the inner wall of the hole 37, and this results in increase in eddy-current loss.
(c) The bonding between the magnetic sleeve and the drum-like magnetic bobbin only by the solder layers 39, 39 and the electrode layers 33, 33' is in some cases mechanically insufficient.
It has also become clear that the above-described (a), (b) and (c) deteriorate in some cases other characteristics of the chip-like inductance element than the Q value.
On the other hand, the completed chip-like inductance element 27 is finally to be mounted to a predetermined location on a printed circuit board by solder connection, and it is preferable to simultaneously mount a plurality of chip elements on a printed circuit board from a viewpoint of achieving lower mounting cost. Such a mounting method will be called a multi-mounting method. In the multi-mounting method, a plurality of chip elements pass through a tube and are dropped into a template having predetermined position-determining holes for elements by a suitable element-supplying hopper. An ultraviolet curing-type resin, for example, has previously been coated on the printed circuit board. The printed circuit board is pressed from below, then is turned upside down and the template is removed, and is subsequently irradiated by an ultraviolet lamp to fix the chip elements. After mounting other electronic components, such as components having leads, on the printed circuit board, all chip elements or electronic components are simultaneously solder connected. The multi-mounting method has an excellent productivity, so it has a feature that the mounting cost is lower as described above. The multi-mounting method cannot be used, however, for conventional square chip-like inductance elements in which the shape of the both side surfaces 36, 36 printed or coated with the electrode layers 33, 33' is square, due to reasons, such as diffuculty in position dermination by the template, so there is a problem that the mounting cost of square chip-like inductance elements becomes high. It is impossible to modify these elements into a cylinder type, because the external electrode layers 33, 33' are located on both end surfaces, and the drum-like bobbin is in a feed-through hole which is parallel to them.
On the other hand, there exists an idea that a hole fed through from the electrode layer 33 to the electrode layer 33' is used for fitting the drum-like magnetic bobbin, and thus it becomes possible to use a cylinder sleeve. However, the above-described problems, such as the penetration of the flux, the eddy-current loss due to adherence of the electrode layers 33, 33' to the inner wall of the hole 37, cannot be solved.